This invention relates to applying a coating, such as paint, of a predetermined constant thickness to all or part of an elongate member, such as an FRP pultruded lineal used to fabricate windows. In the case when the elongate member is pultruded, advantages exists in coating contemporaneously or in-line with the pultrusion process. See U.S. Pat. No. 4,581,722.
Typical systems For applying paint off-line to an advancing elongate member or lineal include spray guns and rollers. These off-line systems for applying usually are not commercially economical.
A recent off-line development shown in U.S. Pat. No. 4,883,690 discloses a lineal coating method using a guide die and a coating die which are generally collinear to receive the advancing elongate member for coating. The patent teaches that a reservoir which is associated with the coating die is to be supplied by a constant pressure feed pump, delivering the paint at a desired pressure and volume. The back pressure in the reservoir is maintained at a high level, so that the reservoir will act as a manifold. The reservoir is in direct contact with the lineal and with the coating passageway.
In still another off-line improvement, U.S. patent application Ser. No. 08/238,071, filed on May 2, 1994, discloses an improved method and apparatus for coating elongated members including the use of a pressurized manifold and a slot or other high aspect ratio conduit for communicating between the manifold and the passageway in the coating die. Since the thin slot restricts the flow of paint, the pressure of paint in the coating die passage way is maintained at low levels even when the reservoir is maintained at high pressure to ensure uniform paint delivery around the part circumference,
A need exists, however, to carry these systems one step farther and paint the lineals on-line. The heat distortion temperatures of most plastic substrates, however, will not tolerate the bake or cure cycle temperatures required for powder coatings, typically 300.degree. F. to 400.degree. F., without the aid of some type of support or backup. Since many lineals require full coating coverage on all surfaces, an external support is not practical and if used would "rob" coating intended for the lineal. Powder coating of lineals or other long pultruded shapes typically would be coated and cured in a vertical position to prevent warpage and distortion. This type of coating facility is very expensive to purchase, maintain and staff.